The present invention relates to a crease-lined packaging laminate comprising at least two layers. The present invention also relates to a method of producing the crease-lined packaging laminate, and also to packaging containers produced from the crease-lined packaging laminate by fold forming.
Use has long been made in the packaging industry of packages of the single-use type for packing and transporting liquid foods. Such so-called single-use disposable packages are often manufactured from a flexible material which, by fold forming and sealing, is converted into filled, sealed packaging containers of the desired shape. A very large group of these disposable packages is produced from a laminated packaging material comprising a core layer of paper or paperboard and outer, liquid-tight coatings of plastic on both sides of the core layer. The packaging laminate may also include additional layers of plastic and/or metal in order to impart to the packaging containers superior barrier properties against, for example, gases and light.
While the packaging material is in the unfolded, planar state, it is often provided with lines of weakness, so-called crease lines, for facilitating folding with the purpose of facilitating the conversion of the packaging material into packaging containers of the desired configuration.
Conventionally, such crease lines are realised by placing the packaging material intended for creasing between moving male and female parts of a creasing tool which, by pressing, deforms and impresses the desired weakening pattern in the packaging material. The deformation takes place in that the packaging material is, along the intended fold lines, pressed into grooves in the female part of the tool by means of linear projections or ridges on the surface of the male tool. A packaging material with crease lines produced in this manner displays a positive and a negative side, i.e. the creasing tool gives rise to an elevated linear (ridge-like) deformation of the one, positive side of the packaging material, and a corresponding linear depression on the other, negative side of the packaging material.
A pattern of such crease lines may be obtained on processing of planar material sheets by means of press plates or by so-called rotation creasing, i.e. creasing of a continuous web by means of two cooperating rotary rollers with complementary channels or grooves and ridges or beads respectively.
The conventional method of realising crease lines makes for a simple folding process with distinct folding lines, but changes in the process entail high costs and extensive work, since each specific crease line pattern and each specific packaging material, with specific thickness and quality, requires its unique creasing tool with adapted widths and depths in the grooves and ridges.
A further drawback inherent in the conventionally crease-lined packaging material is that the folded side edges of the packaging container tend to have a rounded, blunt appearance. On fold forming along the crease line, the raised linear deformation of the packaging material is compressed on the positive side of the packaging material, on the inside of the packaging container, forming ridges or accumulations of packaging material. Since the relatively large accumulation of compressed packaging material is located centrally in the fold, and because of the relative resilience of the fibres gathered in the material accumulation, tensions and forces arise in the fold edge because of the material""s propensity to xe2x80x9cspring backxe2x80x9d to its original planar form. As a result of these resilient return forces, the fold edges of the packaging container will become readily gently rounded with a tendency to be flattened on external loading, for example from the grip of a hand, which gives the package an impression of poor grip rigidity.
A known method of realising better defined folds in a packaging container is described in Swedish Patent Application carrying publication number 467302. By removing the above mentioned raised linear deformation on the positive side of the packaging material, by mechanical processing such as milling, subsequent folding of the packaging material is facilitated at the same time as the material is weakened along the crease line and the return resilience forces in the fold region are reduced. However, this method suffers from the drawbacks that the surface of the packaging material on the inside of the packaging container is locally destroyed in the crease line region, and that the strength of the fold is reduced as a result of the removal of material. Moreover, dust and/or waste material are created which need to be taken care of.
One object of the present invention is therefore to realise a crease-lined packaging material of the type described by way of introduction, without consequential problems of the type intimately related to the prior art techniques and methods.
Another object of the present invention is to realise a crease-lined packaging material of the type described by way of introduction which makes for sharper, better defined folds of the packaging material and thus better formed edge lines and corners in a packaging container.
Yet a further object of the present invention is to provide a method for realising crease lines in a packaging material of the type described by way of introduction, obviating complex, conventional creasing processes using relatively expensive creasing tools, and to make for simpler, more rational and more economical changes of crease line patterns on switching between different package sizes and packaging material qualities.
Still a further object of the present invention is to realise a better formed packaging container possessing improved configurational stability and gripping stability on the action of external forces.
These and other objects are attained by means of a laminated packaging material comprising at least two layers wherein the adhesive bonding strength between the at least two layers is reduced or eliminated along the crease lines of the packaging laminate. One of the layers can be locally treated along the crease lines in order to counteract adhesion of the adjacent layer. The adhesion counteracting agent can be applied between the layers along the crease lines.
Preferably, one of the layers is paper or paperboard. The second layer can be aluminum foil or a greaseproof paper.
A method for producing a crease-lined packaging laminate in accordance with the present invention includes applying an adhesion counteracting agent in the regions of the crease lines between the at least two layers. Another method for producing a crease-lined packaging laminate in accordance with the present invention includes applying an adhesion-promoting agent in the regions outside of the crease lines between the at least two layers. Alternately, the at least two layers are adhered to one another by heating the laminate and an insufficient quantity of heat is applied to the regions of the crease lines.
In practicing these methods, the adhesion-promoting agent can be a UV-curing or EB-curing agent and curing can be carried out by subjecting the laminate to UV- or EB-radiation after the two layer have been laid together. The adhesion can also be carried out by heating the layers wherein the regions of the crease lines absorb an insufficient quantity of heat for adhesion. Differential heating can be carried out by blackening or darkening the surfaces on the at least one layer, leaving the regions of the crease lines white or light and subjecting the laminate to IR-radiation.
In use, the laminate can be used to make packaging containers.
Furthermore, the present invention provides a grip stable packaging container with well-defined side edges which is produced by fold forming of a packaging laminate according to the present invention.
By selectively reducing or eliminating the bonding adhesive strength between the layers in a packaging laminate which comprises at least two such layers, along the linear regions along which the packaging laminate is to be folded, relatively complex, conventional creasing processes using expensive creasing tools can be obviated, at the same time as the fold edges of the packaging container will be more distinct and the packaging container will thereby be given attractive appearance with good handling stability and durability.